1. Field of the Invention
The invention relates to a method and apparatuses for identification of the position of data packets which are located in a serial received data stream.
2. Description of Related Art
Data packets in the transmission system used as the basis here contain a part of fixed length and a part of variable length. The part of fixed length may be called a check field and contains information about the length of the part of variable length.
If the data packets are transmitted via a channel which is noisy, then they can be interfered with on the transmission path, for example in the case of packet-oriented digital radio transmission. Even entire packets may be lost.
However, within the data stream, the starting points and end points of the respective data packets are intended to be detected at the receiver end. In order to make it possible to identify a data packet at the receiver end, that is to say to identify a packet position, a known bit sequence is normally introduced into the data stream at the transmitter end. At the same time, a logic device ensures that bit sequences which are identical to this are eliminated from the data stream. This is normally achieved by means of additional symbols which, admittedly, change the word but leave the useful information to be transmitted otherwise unchanged.
Another option would be to transmit ancillary information as well in the bundle structure of the system which is transmitting the data.
In the case of conventional data transmission, it is furthermore known for the transmission to be checked for errors by inserting a check sum into the data packet to be transmitted, which check sum is formed on the basis of check data which are located in a check field. At the receiver end, a new check sum is then formed in the same manner on the received check data and is compared with the received check sum. If this comparison produces a match, the transmission was error-free.